1. Field of the Invention
The present invention relates to a device and method for controlling a transfer voltage in an electrophotographic recording apparatus for use in a copier, facsimile apparatus, and a printer, and in particular, to a device and method for controlling a transfer voltage to be fed to a transfer roller in synchronization with an exposure signal.
2. Description of the Related Art
In general, a transfer voltage is fed to a transfer roller upon insertion of a paper sheet between the transfer roller and an organic photoconductive (OPC) drum. This can result in unnecessary power dissipation and can reduce the life of the organic photoconductive drum upon application of a high voltage to the organic photoconductive drum, despite the presence of the paper sheet between the organic photoconductive drum and the transfer roller. Another problem that can occur is the possible application of a transfer voltage without proper introduction of the paper sheet between the transfer roller and the organic photoconductive drum which can damage the sensitive surface of the organic photoconductive drum, and further, can degrade the printing quality.
U.S. Pat. No. 4,262,188 to Beach, entitled METHOD AND APPARATUS FOR IMPROVING PRINT QUALITY OF A THERMAL PRINTER, discloses the uniformity of density of characters printed by thermal printers upon thermally sensitive paper is enhanced by controlling the amount of energy supplied to the print head during subsequent printings before the print head has completely cooled to ambient temperature. It is disclosed that to obtain the desired uniformity the energy supplied to the print head for subsequent printings is made proportional to the energy lost by cooling of the print head between printings. It is disclosed this results in the print head being reheated to substantially the same printing temperature for each printing of a character or character segment. By using a dot driver having an R-C circuit that recharges the capacitor between print pulses at a rate that is proportional to the thermal time constant of the print head, it is disclosed that the energy stored by the capacitor can then be used to re-heat, or control the re-heating, of the print head to substantially the same selected print temperature. By maintaining the R-C charging time constant substantially between 0.1 .tau.and .tau. (.tau. is the thermal time constant of the print head) it is disclosed the resultant print character segments have substantially uniform density.
U.S. Pat. No. 4,324,486 to Nishikawa, entitled RECORDING DEVICE INCLUDING A HEATING MEANS, discloses a recording device having a heating unit operated and controlled to a predetermined operating temperature, the start of the recording device being governed so as not to operate the heating unit before its temperature reaches a predetermined operating value, the starting of the recording device being permitted prior to a certain time before the temperature of the heating unit reaches the predetermined operating value after the power supply is energized source for the recording device.
U.S. Pat. No. 4,468,113 to Motohashi et al., entitled TRANSFER TYPE ELECTROSTATIC REPRODUCING APPARATUS, discloses an electrostatic reproducing apparatus provided with a transfer paper thickness detecting element and/or a transfer paper size detecting element and an exposure device between the development device and the transfer device. The quantity of light to be irradiated onto the photosensitive member from the exposure device is disclosed to be adjusted according to a paper thickness information of the paper thickness detecting element and/or a paper size information of the transfer paper size detecting element. The paper thickness detecting element is disclosed to comprise a light emitting element and a light receiving element, and the paper size detecting element is also disclosed to comprise a magnet mounted on a paper feeding cassette and a lead switch mounted on the apparatus body side correspondingly thereto.
U.S. Pat. No. 4,502,056 to Matsuda, entitled TEMPERATURE CONTROL SYSTEM, discloses a temperature control system for a thermal printer which prints by urging a printing plate with type formed thereon against a heat-transfer paper sheet. It is disclosed that the system raises the temperature of the printing plate rapidly after power is turned on and then maintains the temperature of the printing plate essentially constant at the optimal temperature, so that clear printing can be performed at any time. In the initial heating period of the printing plate, a high voltage is applied to the printing plate to raise the temperature quickly. It is disclosed when a first sensor detects that the printing plate has reached a temperature close to the optimal printing temperature, the high voltage supply is interrupted. Thereafter, a second sensor and a control circuit connected thereto are disclosed to serve to produce a low voltage that is applied so as to maintain the printing plate at the optimal printing temperature. It is also disclosed that the magnitude of the low voltage is inversely proportional to printing plate temperature.
U.S. Pat. No. 4,839,695 to Yamamoto et al., entitled DEVICE FOR CONTROLLING CHARGE AREA OF PHOTORECEPTOR, discloses a device for controlling the charge area of a photoreceptor including a detector for detecting the length of a sheet of copying paper, another detector for detecting the length of an image projected area of the photoreceptor, a selecting device for selecting the shorter one between the detected length of the copying paper sheet and that of the image projected area by comparing them with each other, and controls for controlling the charging time of the main charger so as to charge the photoreceptor to an area corresponding to a length selected by the selecting device, whereby the charge area of the photoreceptor is properly controlled so as to correspond to an area necessary to be transferred, even when the length of the image projected area on the photoreceptor differs from that of the coping paper sheet.
U.S. Pat. No. 5,099,287 to Sato, entitled TRANSFERRING VOLTAGE CONTROL SECTION, discloses an electrophotographic printing apparatus including a paper supplying mechanism for supplying recording paper, and a transferring section for charging the recording paper supplied from the paper supplying mechanism by means of a transferring voltage and for transferring development material adhered to the surface of a charging body of the apparatus to the charged recording paper. It is further disclosed that the electrophotographic printing device also includes a transferring voltage control section for controlling the transferring voltage level according to the type of the recording paper.
U.S. Pat. No. 5,155,501 to Fujita et al., entitled ELECTROPHOTOGRAPHIC APPARATUS WITH FREQUENCY AND DUTY RATIO CONTROL, discloses an electrophotographic apparatus wherein a photosensitive body charged by a charger is exposed to light emitted from an exposer, for the formation of an electrostatic latent image, and wherein the electrostatic latent image is developed by a developer and the image developed by the developer is transferred on a paper sheet by a transfer charger. The transfer charger of the apparatus is disclosed to be made up of a converter transformer, a switching circuit for controlling the excitation of the converter transformer, and an error detector, arranged in association with the converter transformer, for detecting an error voltage corresponding to a transfer voltage. The apparatus is disclosed to have a separately (or externally) excited converter which outputs the transfer voltage from the secondary winding of the converter transformer, and input section from which one of the print density levels that are predetermined stepwise is designated, and a control section for controlling the frequency and duty ratio of a transfer signal used for causing the switching circuit to perform a switching action, in accordance with the print density level designated from the input section and the error voltage information supplied from the error detector.
U.S. Pat. No. 5,177,531 to Miyasaka et al., entitled ELECTROSTATIC RECORDER AND ELECTROSTATIC LATENT IMAGE MEASURING INSTRUMENT, discloses an electrostatic recorder including an electrostatic latent image measuring instrument for measuring a state of an electrostatic latent image formed on a photosensitive substance, and executing a printing process until an electrostatic latent image formed on a surface of a photosensitive substance based on measured data is transferred onto a blank form as a visual image by a transfer device by adjusting control factors such as exposure, exposure time, electrostatic charge voltage, development bias, temperature and humidity. It is also disclosed that the electrostatic latent image measuring instrument is provided with distance sensors which, when a measuring electrode is disposed near to the photosensitive substance, maintains a constant distance therebetween.
U.S. Pat. No. 5,250,999 to Kimura et al., entitled IMAGE FORMING APPARATUS HAVING TRANSFER VOLTAGE AND PROCESS SPEED CONTROL, discloses a color image forming apparatus for forming a toner image on a transparent member used in combination with overhead projectors including a speed switch for switching the process speed while an image carrier is rotating, after toner images of a number of colors are formed on the image carrier; a process control for controlling the transfer conditions under which the toner images are transferred onto the recording medium, in response to switching of the process speed; and a selector for selecting an overhead projection mode including a voltage switch for reducing voltage applied to the transfer device after a predetermined time has elapsed. It is also disclosed that the process control preferably includes a fixing temperature control for controlling the fixing temperature of the recording medium having the toner images transferred thereon.
U.S. Pat. No. 5,287,149 to Hoshika, entitled IMAGE FORMING APPARATUS HAVING IMAGE TRANSFER ELECTRODE CONTACTABLE TO TRANSFER MATERIAL, discloses an image forming apparatus including an image bearing member for bearing a toner image, movable along an endless path, an original supporting platen for supporting an original, an illumination source for illuminating an original on the supporting platen, an image forming device including a charger, an exposure optical system, including a reciprocable part for directing a light image of the original on the supporting platen, a developing device and an image transfer device, wherein the reciprocable part moves in a first direction, during an image formation, in which the light image is directed to the image bearing member for image formation thereon and in a second direction, during non-image-formation, for returning the part, and wherein the illumination source emits light both during the image formation an during the non-image-formation to direct the light image to the image bearing member, and wherein a developing bias voltage in the developing device is switched depending on whether the apparatus is in the image formation or in the non-image-formation so that an image formed on the image bearing member is not developed by the developing device during the non-image-formation.
U.S. Pat. No. 5,450,180 to Ohzeki et al., entitled IMAGE FORMING APPARATUS HAVING CONSTANT CURRENT AND VOLTAGE CONTROL IN THE CHARGING AND TRANSFER REGIONS, discloses an image forming apparatus including a movable image bearing member, an image forming device for forming an image on the image bearing member, a charging member disposed opposed to the image bearing member, and bias application device for applying a bias voltage to the charging member, wherein the bias applying device effects a constant voltage control to the charging member when an image area of the image bearing member is in a charging region of the charging member and effects a constant current control during at least a part of a period in which an area of the image bearing member other than the image area is in the charging region, and wherein a level of a constant voltage of the constant voltage control is determined during the constant current control.
U.S. Pat. No. 5,729,267 to Shimada et al., entitled IMAGE FORMING APPARATUS HAVING IMAGE TRANSFER WITH TONER CLEANING FUNCTION, discloses an image forming apparatus having a photosensitive drum, a charger for uniformly charging the photosensitive drum, an exposing means for forming an electro-static latent image on the photosensitive drum, an exposing unit for forming a visual image by developing the electro-static latent image, a transfer roller for transferring the visual image to a printing medium, which includes a transfer voltage supply circuit that supplies the transfer roller one or more times with voltage in one polar direction and successively in the other polar direction during an interval after starting of operation of the image forming apparatus and before the time when the printing medium is transported to the transfer roller.
U.S. Pat. No. 5,812,904 to Rhee et al., entitled IMAGE FORMING APPARATUS AND METHOD FOR CONTROLLING CHARGING POTENTIAL DIFFERENTLY BETWEEN IMAGE FORMING AREA AND NON-IMAGE FORMING AREA OF PHOTOSENSITIVE DRUM, discloses a system for controlling a potential of a photosensitive drum for a laser beam printer having a photosensitive drum on which an electrostatic image is formed, a charger for applying voltages differentially to an image forming area where the photosensitive drum contacts a recording medium and to a non-image forming area where the photosensitive drum does not contact the recording medium to charge the outer surface of the photosensitive drum to a given polarity, a light scanner unit for forming an electrostatic latent image on the drum corresponding to image data, and a developing unit for applying toner onto the photosensitive drum during the image forming area and a transfer charger for transferring a toner image formed on the drum to the recording medium. It is further disclosed that the system also includes a potential controlling unit for applying a first charging potential to the photosensitive drum during the image forming area to charge the photosensitive drum to a given voltage for development, and for applying a second charging potential to the photosensitive drum during the non-image forming area.
U.S. Pat. No. 5,848,321 to Roh et al., entitled METHOD FOR AUTOMATICALLY CONTROLLING TRANSFER VOLTAGE IN PRINTER USING ELECTROPHOTOGRAPHY SYSTEM, discloses an electrophotography machine that produces images of optimum image density regardless of whether an ordinary sheet of paper or a transparency is used as the recording medium. It is disclosed that a photosensor activated in response to the recording media passing a first sensor is positioned on the paper conveyance path and detects whether or not the recording media being processed is an ordinary sheet of paper or a transparency, and that a controller automatically applies the appropriate transfer voltage depending on whether or not the sheet of recording media is a sheet of paper or a transparency.